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a

$\text{When X is joined to Y for a long time then the steady state current through inductor will be I= }\frac{E}{R_1}$ $\text{ Magnetic Energy stored in the inductor is } U = \frac{1}{2} LI^2 = \frac{1}{2} L \frac{E^2}{R_1^2} = \frac{LE^2}{2I_1^2}$ $\text{All this energy will be converted in to heat when X is connected to Z is } H = \frac{LE^2}{2I_1^2}$